Method and apparatus for avoiding or ameliorating cavitation in an asphalt cement fluid circuit

ABSTRACT

A system for dispensing asphalt cement in connection with a working operation on a roadway includes a storage tank for asphalt cement and a working machine having a spray assembly for dispensing the asphalt cement. The system also includes a fluid circuit including a pump that is adapted to pump the asphalt cement from the storage tank to the spray assembly. A controller is operatively connected to the pump and is adapted to control the operation of the pump. A cavitation sensor is provided in the fluid circuit. The cavitation sensor is operatively connected to the controller and is adapted to transmit a cavitation signal to the controller when the cavitation sensor detects conditions in the fluid circuit that are indicative of the existence of cavitation in the pump.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application No. 62/648,152 that was filed on Mar. 26, 2018.

FIELD OF THE INVENTION

This invention relates to a road working process that requires the dispersal of asphalt cement onto a roadway or other surface. More specifically, the invention relates to a method and apparatus for controlling the flow of asphalt cement from a supply tank in order to avoid or ameliorate cavitation in the asphalt cement fluid circuit.

BACKGROUND AND DESCRIPTION OF THE PRIOR ART

Road work is typically carried out by working machines that carry one or more working components and travel along a roadway. Many such working machines are employed to dispense asphalt cement onto the roadway or onto materials to be deposited on the roadway in connection with the performance of road work.

Roadways in the United States are often constructed by preparing and stabilizing the underlying ground structure, building a road base with crushed stone, and then paving over the road base with asphalt paving materials. It is frequently desirable, in the asphalt paving process, to apply a type of asphalt cement (commonly referred to as “tack” or “tack material”) onto the surface of the roadway prior to applying and compacting the asphalt paving material in order to assist in binding the asphalt paving material to the underlying road base. Tack material may be applied by a tack distributor truck, a working machine comprising a self-propelled vehicle with a storage tank for asphalt cement and a spray assembly for dispensing the asphalt cement across the roadway. In the alternative, an asphalt paving machine, another working machine, may include a tack spray assembly that is employed to apply tack material to the roadway prior to the deposition of asphalt paving materials. The paving machine is self-propelled and driven by a wheeled or track drive system. In a common type of paving machine, an asphalt receiving hopper is located at the front end of the machine to receive asphalt paving material from a truck or material transfer vehicle, and a hopper conveyor located below the asphalt receiving hopper transfers the asphalt paving material from the hopper to a transverse distributing auger assembly that is mounted near the rear of the machine. The asphalt paving material is deposited onto and across the roadway or other surface to be paved by the distributing auger assembly, and a floating screed located at the rear end of the machine behind the distributing auger assembly compacts the asphalt paving material to form an asphalt mat. When the asphalt paving machine is configured to apply tack material, this material is typically dispensed onto the surface to be paved from a spray assembly that extends transversely across the width of the machine in front of the distributing auger assembly.

Cold in-place recycling (“CIR”) is a process by which damaged layers of asphalt pavement are removed, and the removed material is processed, additional asphalt cement is added, and the blend or mixture of processed material and asphalt cement is placed on the roadway and compacted. If a roadway has good structural strength, a CIR process can be effective for treating all types of cracking, ruts and holes in asphalt pavement. CIR can be used to repair asphalt roadways damaged by fatigue (alligator) cracking, bleeding (of excess asphalt cement), block cracking, corrugation and shoving, joint reflective cracking, longitudinal cracking, patching, polished aggregate, potholes, raveling, rutting, slippage cracking, stripping and transverse (thermal) cracking. The root cause of the pavement failure should always be investigated to rule out base failure. However, CIR can almost always be used when there is no damage to the base of the roadway. Generally, CIR is only half as expensive as hot mix paving (i.e., paving with new asphalt paving material) while providing approximately 80% of the strength of hot mix paving.

CIR can be carried out by a milling machine or cold planer that is modified for use for cold in-place recycling. Such a machine comprises a wheel-driven or track-driven vehicle that is provided with a working drum that includes a plurality of cutting teeth. The drum is mounted in a housing on the frame of the machine and is adapted to be lowered into contact with the road surface and rotated about a generally horizontal axis so as to cut into the surface to a desired depth as the machine is advanced along the roadway. A spray assembly for asphalt cement is provided to dispense asphalt cement into the drum housing. The asphalt cement is then thoroughly mixed with the milled material by the milling drum and can be left in a windrow or conveyed by a discharge conveyor on the milling machine directly into an asphalt paving machine. Steerable track or wheel drive assemblies are provided to drive the milling machine and to steer it in a desired working direction. Power for driving the milling machine and for operating its systems is typically provided by a diesel engine.

Another type of working machine is a road stabilizer/reclaimer machine. This machine is a type of milling machine that is similar to a cold planer in that it comprises a wheel-driven or track-driven vehicle which includes a milling assembly comprising a milling drum with a plurality of cutter teeth mounted thereon which is contained within a milling drum housing and is adapted to be rotated about a generally horizontal axis. However, the milling drum of a road stabilizer/reclaimer machine is generally employed to mill or pulverize an existing road bed or roadway to a greater depth than does a cold planer prior to initial paving (usually called stabilizing) or prior to repaving (usually called reclaiming), and it leaves the pulverized material in place. A road stabilizer/reclaimer machine may be provided with a spray assembly for asphalt cement, similar to that provided in a cold planer used in a CIR process, to dispense asphalt cement into the drum housing onto the pulverized material in order to stabilize the road bed or other surface, or as part of a CIR process.

When a CIR process is carried out with a modified milling machine or a road stabilizer/reclaimer machine and an asphalt paving machine, the asphalt cement component of the mixture must be supplied from a separate supply tank truck that is coupled to the modified milling machine or road stabilizer/reclaimer machine. The asphalt cement component is drawn directly from the tank on the supply truck and pumped through a flow system comprising an asphalt cement circuit to the spray assembly in the milling drum housing.

Sometimes the CIR process is carried out with a milling machine or stabilizer/reclaimer in train with a cold recycler machine such as the RT-500 that is made and sold by Roadtec, Inc. of Chattanooga, Tenn. The cold recycler machine may include a vibratory screen, a crusher, an onboard source of asphalt cement and a pugmill mixer. When the CIR process is carried out using a cold recycler machine, the recycled asphalt material that is milled by the milling machine is transferred to the vibratory screen and then to the crusher on the cold recycler machine, and the screened and crushed material is then mixed with asphalt cement that is dispensed by a spray assembly from an onboard supply tank into the pugmill. In either configuration of equipment used in a CIR process, the primary component of the new pavement is asphalt paving material that is already in place on the roadway. The only other component of the new pavement is the asphalt cement carried by the cold recycler machine or by a supply truck. Since the rate of advance of the equipment engaged in the CIR process is determined primarily by the rate of advance of the milling machine, it is common for all of the components of the CIR process except for the asphalt paving machine to be coupled together so as to move at the same rate during all phases of the CIR process. Such components are frequently referred to as a CIR train.

Yet another type of working machine that may be employed to dispense asphalt cement onto a roadway is a modified chip spreader which is used in a chip sealing process. In the conventional chip sealing process, a tack distributor truck applies asphalt cement onto the roadway, and a conventional chip spreader follows to spread a layer of stone chips of high durability and high fracture plane characteristics onto the asphalt cement on the roadway. The conventional chip spreader is a self-propelled vehicle that has a hitch assembly on its rear end for coupling it to the rear end of a chip supply dump truck. The conventional chip spreader has a receiving hopper on its rear end that is adapted to receive chips when the dump bed of the supply truck is raised. However, the receiving hopper can only accommodate a portion of the load of the supply truck, so the conventional chip spreader will pull the dump truck backwards as chips are conveyed from the receiving hopper to a chip spreader assembly on the front end of the chip spreader.

A modified chip spreader comprises a vehicular chip spreading machine which has been modified by the addition of an asphalt cement dispersal system including a spray assembly that is mounted in front of the chip spreader to dispense asphalt cement across the surface of the roadway. The modified chip spreader is a self-propelled vehicle that has a receiving hopper on its front end, a spreader assembly including a spreader hopper on its rear end, and a conveyor assembly for conveying stone chips from the receiving hopper to the spreader assembly. The modified chip spreader also includes an asphalt cement spray assembly that is in fluid communication with an outlet line from an asphalt cement supply truck, which spray assembly is adapted to dispense asphalt cement onto the surface of a roadway in front of the spreader assembly. Preferably, the modified chip spreader also has a pump that is adapted to pump asphalt cement from the asphalt cement supply truck to the spray assembly. The modified chip spreader also has a tow bar on its rear end that is attached to a tow-bar hitch assembly on the front end of an asphalt cement supply truck, and a hitch assembly on its front end for coupling it to rear end of the chip supply dump truck. When the chip supply dump truck and the asphalt cement supply truck are operatively attached to the modified chip spreader, and the dump bed of the chip supply truck is raised, stone chips will fall into the receiving hopper of the modified chip spreader. As the modified chip spreader is driven along the roadway in the chip spreading direction, pushing the chip supply dump truck and pulling the asphalt cement supply truck, the conveyor assembly is operated to convey stone chips to the spreader assembly, and the asphalt cement pump is operated to pump asphalt cement from the asphalt cement supply truck to the spray assembly. The spray assembly will dispense asphalt cement onto the roadway and the spreader assembly will dispense stone chips onto the newly applied asphalt cement on the roadway.

The various spray assemblies that are found on road working machines including tack distributor trucks, asphalt paving machines, modified milling machines, stabilizer/reclaimer machines, cold recycler machines and modified chip spreaders are in fluid communication with an asphalt cement supply tank which is mounted on the machine itself or is carried by a separate supply truck. This fluid communication comprises an asphalt cement fluid circuit having a pump for drawing the asphalt cement out of the supply tank and suitable piping and conduits for conveying the asphalt cement to the spray assembly. As the asphalt cement in the supply tank is depleted, or as the slope of the roadway on which the road work is being carried out changes (so that the slope of the level of asphalt cement in the supply tank changes), it is possible for air to enter the inlet (suction) side of the pump. When this occurs, cavitation may occur within the pump. Cavitation is undesirable because it produces extensive erosion of the internal pump components, additional noise from the resultant vibrations, and a significant reduction of efficiency because it distorts the flow pattern through the pump. Cavitation may cause the flow of asphalt cement to be interrupted or intermittent. It may cause degradation of the asphalt cement and/or damage to the pump. Consequently, it would be desirable if a method and apparatus could be provided for controlling the dispersal of asphalt cement through the asphalt cement fluid circuit that would minimize the risk of cavitation.

ADVANTAGES OF A PREFERRED EMBODIMENT OF THE INVENTION

Among the advantages of a preferred embodiment of this invention is that it provides a method and apparatus for controlling the dispersal of asphalt cement through the asphalt cement fluid circuit of a working machine that includes an asphalt cement spray assembly in such a manner as to minimize the risk of cavitation in the pump that is part of the fluid circuit. Additional objects and advantages of this invention will become apparent from an examination of the drawings and the ensuing description.

NOTES ON CONSTRUCTION

The use of the terms “a”, “an”, “the” and similar terms in the context of describing the invention are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising”, “having”, “including” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. The terms “substantially”, “generally” and other words of degree are relative modifiers intended to indicate permissible variation from the characteristic so modified. The use of such terms in describing a physical or functional characteristic of the invention is not intended to limit such characteristic to the absolute value which the term modifies, but rather to provide an approximation of the value of such physical or functional characteristic. All methods described herein can be performed in any suitable order unless otherwise specified herein or clearly indicated by context.

Terms concerning attachments, coupling and the like, such as “attached”, “connected” and “interconnected”, refer to a relationship wherein structures or components are secured or attached to one another either directly or indirectly through intervening structures, as well as both moveable and rigid attachments or relationships, unless otherwise specified herein or clearly indicated as having a different relationship by context. The terms “operatively attached” and “operatively connected” describe such an attachment, coupling or connection that allows the pertinent structures or components to operate as intended by virtue of that relationship. The term “fluid communication” is such an attachment, coupling or connection that allows for flow of fluid from one such structure or component to or by means of the other.

The use of any and all examples or exemplary language (e.g., “such as” and “preferably”) herein is intended merely to better illuminate the invention and the preferred embodiments thereof, and not to place a limitation on the scope of the invention. Nothing in the specification should be construed as indicating any element as essential to the practice of the invention unless so stated with specificity. Several terms are specifically defined herein. These terms are to be given their broadest reasonable construction consistent with such definitions, as follows:

The term “asphalt cement” and similar terms refer to a bituminous fluid that is used in combination with aggregate materials in the production of asphalt paving materials, or as a tack material. The term “asphalt cement” includes asphalt emulsions which are chemically stabilized dispersions of asphalt cement in water.

The term “asphalt paving material(s)” and similar terms refer to a bituminous paving mixture that is produced, using asphalt cement and any of various aggregate materials.

The terms “asphalt paving machine” and “paver” refer to a working machine for applying asphalt paving material to form an asphalt mat on a roadway, parking lot or similar surface. An asphalt paving machine or paver is typically a self-propelled vehicle having a hopper at one end for receiving asphalt paving material and a floating screed at the other end for forming an asphalt mat.

The term “milling machine” refers to a working machine comprising a self-propelled vehicle including a milling or working drum that is adapted to be placed into contact with a roadway or road base surface for removing a portion of the surface. The term “milling machine” includes but is not limited to machines that are sometimes referred to as cold planers, road stabilizers and roadway reclaiming machines. The term “milling machine” also includes a modified milling machine that is used in a CIR process.

The term “CIR process” refers to a use of cold in-place recycling equipment to repair damage to a roadway, by removing layers of asphalt pavement, adding asphalt cement to the asphalt paving material so removed, placing the mixture of asphalt cement and asphalt paving material onto the roadway, and compacting it.

The term “modified milling machine” refers to a milling machine which has been modified by the addition of an asphalt cement fluid circuit including a spray assembly that is adapted to dispense asphalt cement onto milled material within or adjacent to a housing assembly for the milling drum.

The term “working machine” refers to a road working machine comprising a self-propelled vehicle or mobile support that includes a spray assembly for use in dispensing asphalt cement onto a roadway, or to a road working machine that includes a spray assembly for use in dispensing asphalt cement onto aggregate materials in a CIR process.

The term “working operation” refers to the operation of a working machine on a roadway.

The term “downstream”, as used herein to describe a relative position on or in connection with an asphalt cement fluid circuit that is part of a working machine having an asphalt cement spray assembly, refers to a relative position in the direction of the flow of asphalt cement towards the spray assembly.

The term “upstream”, as used herein to describe a relative position on or in connection with an asphalt cement fluid circuit that is part of a working machine having an asphalt cement spray assembly, refers to a relative position in a direction that is opposite to the direction of the flow of asphalt cement towards the spray assembly.

SUMMARY OF THE INVENTION

The invention comprises a method and apparatus for preventing or ameliorating cavitation in the pump that is part of a fluid circuit for asphalt cement that is associated with a working machine. The working machine includes or is associated with a storage tank for asphalt cement, and it also includes a spray assembly for dispensing asphalt cement. A fluid circuit is provided including a pump by which the asphalt cement is pumped from the storage tank to the spray assembly. A cavitation sensor is provided in the fluid circuit on the suction side of the pump (i.e., upstream of the pump inlet). Preferably, the cavitation sensor is adapted to sense changes in frequency that are associated or are indicative with the existence of cavitation in the pump in the fluid circuit.

More particularly, the invention comprises a system for dispensing asphalt cement in connection with a working operation on a roadway. This system comprises a storage tank for asphalt cement and a working machine comprising a spray assembly for dispensing the asphalt cement. The system further comprises a fluid circuit including a pump having a suction side, which pump is adapted to pump the asphalt cement from the storage tank to the spray assembly. A controller is operatively connected to the pump and is adapted to control the operation of the pump, and a cavitation sensor is provided in the fluid circuit, preferably on the suction side of the pump. The cavitation sensor is operatively connected to the controller and is adapted to transmit a cavitation signal to the controller when the cavitation sensor detects conditions in the fluid circuit that are indicative of cavitation in the pump.

In some embodiments of the invention, the cavitation sensor may comprise an accelerometer or other vibration sensor. The cavitation sensor is operatively connected to a controller in the working machine and is adapted to send a cavitation signal to the controller when cavitation (or a condition consistent with the presence of cavitation) in the pump is detected. The controller is also operatively connected to the pump and to other systems in the working machine and is adapted to stop the operation of the pump and/or to signal the operator of the working machine when it receives a cavitation signal from the cavitation sensor.

In order to facilitate an understanding of the invention, a preferred embodiment of the invention, as well as the best mode known by the inventor for carrying out the invention, is illustrated in the drawings, and a detailed description thereof follows. It is not intended, however, that the invention be limited to the particular embodiment described or to use in connection with the apparatus illustrated herein. Therefore, the scope of the invention contemplated by the inventor includes all equivalents of the subject matter recited in the claims, as well as various modifications and alternative embodiments such as would ordinarily occur to one skilled in the art to which the invention relates. The inventor expects skilled artisans to employ such variations as seem to them appropriate, including the practice of the invention otherwise than as specifically described herein. In addition, any combination of the elements and components of the invention described herein in any possible variation is encompassed by the invention, unless otherwise indicated herein or clearly excluded by context.

BRIEF DESCRIPTION OF THE DRAWINGS

The presently preferred embodiment of the invention is illustrated in the accompanying drawings, in which like reference numerals represent like parts throughout, and in which:

FIG. 1 is a side view of a portion of a modified milling machine which is attached to an asphalt cement supply truck, showing the supply truck on a first slope “S₁” and illustrating a level “L₁” of asphalt cement in the tank of the supply truck which is unlikely to produce cavitation in the pump associated with the modified milling machine.

FIG. 2 is a side view of the portion of the modified milling machine and asphalt cement supply truck shown in FIG. 2, illustrating the supply truck on a second slope “S₂” and showing a level “L₂” of asphalt cement in the tank of the supply truck which could produce cavitation in the pump associated with the modified milling machine.

FIG. 3 is a front view of a pump that is part of a preferred embodiment of the asphalt cement fluid circuit of a working machine, to which a cavitation sensor is attached.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

This description of a preferred embodiment of the invention is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description of this invention. The drawings are not necessarily to scale, and certain features of the invention may be shown exaggerated in scale or in somewhat schematic form in the interest of clarity and conciseness.

The invention comprises a method and apparatus for preventing or ameliorating cavitation in the fluid circuit for asphalt cement that is associated with a working machine such as modified milling machine 10, shown in FIGS. 1 and 2. Modified milling machine 10 includes milling drum 12 which is enclosed in a milling drum housing (not shown). Modified milling machine 10 is mechanically coupled by tow bar 14 to asphalt cement supply truck 16 which includes asphalt cement storage tank 18. As shown in these drawings, modified milling machine 10 and asphalt cement supply truck 16 are coupled together for use in a CIR process. An asphalt cement fluid circuit is provided including asphalt cement supply line 20 from storage tank 18, pump assembly 22 and suitable piping or hoses known to those having ordinary skill in the art to which the invention relates for conveying the asphalt cement from pump assembly 22 to spray assembly 24 that is located adjacent to milling drum 12 within the milling drum housing of modified milling machine 10. A cavitation sensor, preferably accelerometer 26, is mounted on or adjacent to pump 28 (both of which are shown in FIG. 3) of pump assembly 22, preferably on the inlet or suction side of the pump. Asphalt cement supply line 20 from asphalt cement storage tank 18 is attached to inlet conduit 30 of pump 28, and outlet line 32 from pump 28 conducts asphalt cement to spray assembly 24. In other embodiments of the invention, a cavitation sensor may be mounted within or on pump 28 or in another convenient location. In still other embodiments of the invention, the cavitation sensor may comprise a vibration sensor or other component that is mounted on or in the asphalt cement fluid circuit which is capable of detecting cavitation within the pump. Modified milling machine 10 includes operator's station 34 and controller 36 which is located in or adjacent to the operating station.

In FIG. 1, supply truck 16 is coupled to modified milling machine 10, and both are shown in operation on a first slope “S₁”, thereby producing a level “L₁” of asphalt cement in tank 18 of the supply truck, which condition is unlikely to produce cavitation in the pump associated with modified milling machine 10. FIG. 2 shows modified milling machine 10 and supply truck 16 in operation on a second slope “S₂”, which produces a level “L₂” of asphalt cement in the tank of the supply truck. Such a level would be likely to produce cavitation in the pump associated with the modified milling machine.

In the embodiment of the invention illustrated in the drawings, accelerometer 26 is provided in the fluid circuit on the suction side of pump 28, i.e., upstream of pump inlet 38. Preferably, the cavitation sensor comprises a Model 628F01 accelerometer that is sold by PCB Piezotronics of Depew, N.Y. This preferred cavitation sensor is adapted to sense changes in frequency that are associated with cavitation within the fluid circuit. Accelerometer 26 is operatively connected to controller 36 in the working machine by means of output signal/power line 40 and is electrically grounded through ground line 42. Accelerometer 26 is adapted to send a signal to the controller when cavitation is detected in pump 28 or in the asphalt cement fluid circuit adjacent to pump 28.

A preferred embodiment of the cavitation sensor comprises an accelerometer or other vibration sensor that may be used to measure the change in amplitude and frequency of the fluid moving within the asphalt cement fluid circuit, and/or how fast the fluid accelerates from one direction to another, thereby producing vibration within the fluid circuit. The measurement of such changes in frequency and amplitude can indicate the presence of cavitation in the pump.

Preferably, accelerometer 26 is adapted to send a signal to controller 36 when it detects a frequency range displacement within the range of 3-40 Hz and/or an output range DC displacement (peak to peak) within the range of 0-0.254 mm. Controller 36 is also operatively connected to pump 28 and to other systems in the working machine. Controller 36 is adapted to control the operation of pump 28, and more particularly, it is adapted to stop the operation of the pump and/or to signal the operator of the working machine when cavitation is detected.

Controller 36 may embody a single microprocessor or multiple microprocessors that include components for controlling pump 28 and other operations of modified milling machine 10 based on input from an operator of the modified milling machine and on sensed or other known operational parameters. Controller 36 may include a memory, a secondary storage device, a processor and other components for running an application. Preferably, controller 36 is operatively connected to an onboard viewing screen which is adapted to display to an operator signals indicative of the operation of pump 28, as well as other information about the operation and use of modified milling machine 10 that is calculated or determined by the controller. The controller may also include a wireless transmitter (and an associated signal booster) which is adapted to transmit to an external receiver (such as a computer or cellular telephone) signals indicative of the operation of pump 28, as well as other information measured or determined by the controller. Various other circuits may be associated with controller 36 such as power supply circuitry, signal conditioning circuitry, solenoid driver circuitry and other types of circuitry. Numerous commercially available microprocessors can be configured to perform the functions of controller 36. It should be appreciated that controller 36 could readily be embodied in a general purpose computer or machine microprocessor capable of controlling numerous machine functions of modified milling machine 10.

The invention thus provides a system for detecting cavitation or conditions indicative of cavitation in the fluid circuit for asphalt cement that is associated with a working machine having a spray assembly for asphalt cement. A cavitation sensor is provided in the asphalt cement fluid circuit and is operatively connected to a controller in the working machine. The cavitation sensor is adapted to send a cavitation signal to the controller when cavitation is detected. The controller is also operatively connected to the pump in the fluid circuit for asphalt cement, and to other systems in the working machine. The controller is adapted to stop the operation of the pump and/or to transmit a cavitation existence signal to operator's station 34 of the working machine when cavitation is detected.

Although this description contains many specifics, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments thereof, as well as the best mode contemplated by the inventor of carrying out the invention. The invention, as described and claimed herein, is susceptible to various modifications and adaptations as would be appreciated by those having ordinary skill in the art to which the invention relates. 

What is claimed is:
 1. A system for dispensing asphalt cement in connection with a working operation on a roadway, said system comprising: (a) a storage tank for asphalt cement; (b) a working machine comprising a spray assembly for dispensing the asphalt cement; (c) an asphalt cement fluid circuit including a pump having a suction side, said pump being adapted to pump the asphalt cement from the storage tank to the spray assembly; (d) a controller that is operatively connected to the pump and is adapted to control the operation of the pump; (e) a cavitation sensor that is provided in the asphalt cement fluid circuit, said cavitation sensor being operatively connected to the controller and being adapted to transmit a cavitation signal to the controller when the cavitation sensor detects conditions in the asphalt cement fluid circuit that are indicative of the existence of cavitation in the pump.
 2. The system of claim 1 wherein: (a) the pump has a suction side; (b) the cavitation sensor is provided in the fluid circuit on the suction side of the pump.
 3. The system of claim 1 wherein the controller is adapted to stop the operation of the pump when it receives a cavitation signal from the cavitation sensor.
 4. The system of claim 1 wherein: (a) the working machine includes an operator's station from which an operator can operate and monitor the components of the working machine; (b) the controller is operatively connected to the operator's station and is adapted to send a cavitation existence signal to the operator's station when it receives a cavitation signal from the cavitation sensor.
 5. The system of claim 1 wherein the cavitation sensor comprises an accelerometer that is adapted to measure the acceleration of asphalt cement in the asphalt cement fluid circuit.
 6. The system of claim 1 wherein the cavitation sensor is adapted to detect vibration within the pump of the asphalt cement fluid circuit.
 7. The system of claim 1 wherein the cavitation sensor comprises an accelerometer that is adapted to measure the change in frequency of the fluid moving within the asphalt cement fluid circuit.
 8. The system of claim 7 wherein the cavitation sensor is adapted to send a signal to the controller when it detects a frequency range displacement within the range of 3-40 Hz.
 9. The system of claim 1 wherein the cavitation sensor comprises an accelerometer that is adapted to measure the change in amplitude of the fluid moving within the asphalt cement fluid circuit.
 10. The system of claim 9 wherein the cavitation sensor is adapted to send a signal to the controller when it detects an amplitude change in peak to peak displacement that is within the range of 0-0.254 mm. 